This invention relates to detectors for detecting the rotational position of the crankshaft of an internal combustion engine, and more particularly to such rotational position detectors which are capable of determining the position of the crankshaft in relation to the respective cylinders of a multi-cylinder engine.
It is becoming increasingly common in the automotive engines to control the ignition or the fuel injection system by means of a microcomputer. In such control of the ignition or the fuel injection system by means of a computer, precise detection of the rotational position of the crankshaft is essential. Thus, computer-based engine control systems are generally provided with a rotational position signal generator for detecting the rotation of the cramshaft or the crankshaft of the engine. In the case of multi-cylinder engines, the rotational position signal generally comprises pulses which respectively correspond to the position of the crankshaft in relation to the respective cylinders; thus, for the purpose of identifying which pulse corresponds to which cylinder, a reference or cylinder-identifying signal which discriminates those pulses corresponding to a particular reference cylinder must also be provided.
FIGS. 1 and 2 show an example of a rotational position signal generator for detecting the position of the crankshaft of a four-cylinder four-stroke internal combustion engine. In FIG. 1, a shaft 1 of the signal generator, coupled, for example, to the camshaft of the engine, rotates in synchrony with the crankshaft, to complete one revolution (360 degrees) as the crankshaft makes two revolutions (720 degrees). In this connection, let us note that a four-stroke engine completes a complete cycle of suction, compression, combustion, and exhaustion in two revolutions (or the rotation of 720 degrees) of the crankshaft. A rotor disk 2 mounted on the shaft 1 has four elongated windows 3 formed at a predetermined radial distance from the center at four circumferential locations corresponding to the predetermined rotational positions of the crankshaft in relation to the respective four cylinders of the engine. The disk 2 further comprises an elongated window 3a for identifying a particular cylinder (hereinafter, cylinder No. 1). The light emitted from a light-emitting diode 4 is received by a photodiode 5 via the windows 3 when they pass therebetween; similarly, the light emitted from a light-emitting diode 4a is received by a photodiode 5a when the window 3a passes therebetween. As shown in FIG. 2, the output signal of the photodiode 5 or 5a is amplified by an amplifier circuit 6, to be supplied to an output transistor 7 having an open collector.
FIG. 3 shows the waveforms of the two output signals of the signal generator of FIG. 1: the cylinder-identifying signal SGC shown at the top row (a) originates from the photodiode 5a; on the other hand, the crankshaft rotational position signal SGT shown below at (b) originates from the photodiode 5. The crankshaft position signal SGT comprises pulses whose leading and trailing edges correspond to the first and second predetermined rotational positions (e.g., 75 degrees and 5 degrees before the top dead center (BTDC) between the compression and the combustion (i.e., power) stroke) of the crankshaft with respect to the respective four cylinders. On the other hand, the cylinder-identifying signal SGC consists of pulses which are generated in synchrony with those pulses of the position signal SGT that correspond to the cylinder No. 1 (the particular or specified cylinder); thus, the pulses of the cylinder-identifying signal SGC are utilized to identify those pulses of the position signal SGT that correspond to the cylinder No. 1.
As shown further in FIG. 4, these output signals SGC and SGT of the rotational position signal generator 8 are supplied via an interface circuit 9 to the microcomputer 10 which controls the ignition and the fuel injection system, etc. With the help of the cylinder-identifying signal SGC, the microcomputer 10 can determine which one of the pulses of the position signal SGT corresponds to which one of the cylinders of the engine; thus, it can correctly determine the ignition timing, etc., of respective cylinders on the basis of the output signals SGC and SGT of the signal generator 8.
The above type of rotational position detectors, however, has the following disadvantage. Namely, since the rotational position signal generator must be provided with two separate and distinct signal generating systems for generating the two signals (i.e., the crankshaft rotational position signal SGT and the cylinder-identifying signal SGC), the organization thereof becomes complicated and the production cost is increased.